The present invention relates to a data correcting device for use with a computed tomography (CT) apparatus. More particularly, the present invention relates to a device with which the data of measurement in a CT apparatus such as a positron or X-ray CT apparatus is automatically corrected whenever a subject under examination moves his body.
Examination with a positron CT apparatus and other CT apparatus usually takes from several tens of minutes to several hours, during which time a subject must remain in the same posture. If he moves at any instant of the examination, data is disturbed and the image reconstructed from the disturbed data either appears blurred or contains an unnatural noise pattern called an "artifact".
This problem has conventionally been solved by two methods. In one method, the part of the subject to be examined is fixed as long as the examination continues. In the other method, the operator monitors the subject with a TV camera or some other suitable device and returns his body to the correct position as soon as a body movement is detected.
In the first method, the subject's body is fixed to the bed with belts or his head to be examined is fixed with a mask.
A typical method of monitoring the subject is shown in FIG. 7. Before starting a measurement, the subject is imaged with a TV camera and displayed as a still image (indicated by the solid line). If the subject's body moves during the measurement, the resulting image is superposed on the still image (as shown by the dashed line) and either the operator or the subject himself makes the necessary adjustment to bring the current image into registry with the still image.
The first approach in which the subject is fixed as long as the measurement continues involves painful procedures and is not applicable to a subject suffering from a disease. Further, the fixing of the subject is by no means perfect and inevitable movements of the subject's body have deteriorated the reconstructed image. In addition, if a measurement is conducted to obtain cerebrophysiological findings, the fixing of the subject causes him a pain and the data acquired might not reflect the normal functions of the brain.
The second approach in which the subject is monitored is principally intended for avoiding a movement of the subject's body and he must be fixed in order to provide a perfect solution by this approach. Further, data obtained when the body moves is not useful at all. In particular, this causes a serious problem in observing the time-dependent change in the distribution of an isotope in the body.